Called volcanic lakes , these bodies of water form either in the craters that are left after a volcano explodes, the calderas left after a volcanic peak or flank collapses, or after lava, ash or mud from volcanoes dam up rivers and streams.

It's a well-known fact that volcanic lakes could release carbon dioxide. Twenty-five years ago, a volcanic lake in Cameroon, Lake Nyos, released lethally high levels of the gas, killing 1,700 people in the surrounding area. This and other tragic incidents revealed that such lakes could be major sources of the global warming gas, which is most likely given off by magma underneath these lakes or rocks heated by such magma.

To see just how much carbon dioxide volcanic lakes as a whole might belch out, scientists randomly sampled 24 volcanic lakes in Nicaragua, Guatemala, El Salvador, Costa Rica, Japan, Cameroon, the Philippines, France and Germany with sensors floating in miniature inner tubes. They next used their findings to project how much of the gas the estimated 769 volcanic lakes worldwide belch out each year.

These new numbers from volcanic regions pale in comparison with the amount of carbon dioxide released by fossil fuel combustion annually an estimated 29.7 billion metric tons in 2007.

Nevertheless, a better understanding and quantification of the amount of gas that volcanic regions put out "is still necessary for understanding global carbon budget modeling," said study researcher Nemesio Perez, a geochemist at the Technological Institute of Renewable Energy in Spain. "And having more precise information on the global carbon cycle and its implications on the present-day atmospheric carbon dioxide budget is important for the climate models."

The scientists detailed their findings in the March issue of the journal Geology.

Charles Q. Choi

Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.